The present invention relates to disk drive storage systems for digital computers.
Rotating magnetic data storage devices have been used in computer systems for over 25 years. Rotatable fixed and removable hard disks having magnetic surfaces have been employed for the recording and retrieval of data. The disk drives have a magnetic read/write head attached to a movable arm used to position the head over a selected concentric track. More recent developments have included utilization of removable flexible disks being comprised of a magnetically coated circular disk of mylar or other flexible material having a diameter of approximately 20.3 centimeters. Devices incorporating these flexible disks are more compact and have a much lower cost per drive than their predecessors using hard disks. One of the most recent developments in magnetic storage devices is the development of flexible mini-disks, the disks comprising a magnetically coated circular flexible plastic disk contained within a rigid envelope having cutouts for accessing the magnetic medium, the mini-disk having an outside diameter of approximately 13.3 centimeters. While these devices offer a further improvement in compactness and reduction in cost per disk drive, the cost per bit stored remains relatively high due to the fact that only a single mini-disk is driven by a mini-disk drive. Furthermore, the recording density of the mini-disk is restricted due to the fact that the number of concentric tracks or track density, is limited. This limitation results from error inherent in the means utilized in seeking the selected tracks. Finally, because the mini-disks are removable, the head-load pressure pad for contacting the surface of the mini-disk with the magnetic read/write head must be positioned a considerable distance from the disk in order to allow the disk to be inserted and removed without interference. This distance between the pressure pad and the disk results in significant delays in head-load time with concomitant increases in the mean time to seek a selected track. To summarize, currently available flexible mini-disk drives have inherent limitations in storage capacity and track seeking speed.